This invention relates to a fuel supply control method for internal combustion engines after starting, and more particularly to a method of this kind which is adapted to control a fuel increment for a fuel quantity supplied to an internal combustion engine immediately after being started, to a proper value dependent upon the temperature of an intake system of the engine.
Conventionally, a fuel supply control method for internal combustion engines after starting has been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 62-93443 owned by the assignee of the present application, wherein the initial value of a fuel increment is set to a value dependent upon the temperature of the engine immediately after starting thereof, then the fuel increment is progressively decreased from the initial value thereof thus set at a predetermined rate, and a fuel quantity corrected by the fuel increment thus decreased is supplied to the engine, to thereby prevent engine stalling after starting of the engine and achieve smooth transition of the engine operation to an accelerating condition immediately after starting of the engine.
However, the above proposed method has the disadvantage that fuel supply cannot be properly effected immediately after starting of the engine when the engine coolant temperature is high at the start of the engine. More specifically, if the engine coolant temperature is already high at the start of the engine, the period of time after the start of the engine and until the engine coolant temperature increases to such a high level that it is no longer necessary to effect the after-start fuel increasing is very short. Accordingly, after such hot starting of the engine the fuel quantity need not be increased by such an amount as required when the engine is started in a cold state, to overcome engine load during warming-up of the engine. Particularly, in the event that the engine is restarted soon after it has been stopped, the temperature of fuel within the intake system of the engine such as fuel injection valves is often so high that gas bubbles are formed in the fuel within the intake system, causing leaning of the mixture supplied to the engine. To prevent leaning of the mixture after hot starting of the engine, however, it suffices to remove gas bubbles from the fuel within the intake system but it is not necessary to increase the fuel quantity. However, according to the aforesaid proposed method, the fuel increasing period after the start of the engine is not set to a value dependent upon the temperature of the engine upon starting in a hot state, that is, even after the start of the engine in a hot state the after-start fuel increasing is effected over a long period of time which is appropriate to engine starting in a cold or normal temperature state, which results in overriching of the mixture supplied to the engine and increased fuel consumption.